There is conventionally disclosed a polycrystalline silicon rod obtained such that gas containing silicon is thermally decomposed or is reduced by hydrogen under the condition of high temperature so that high purity silicon is deposited on a filament rod (see e.g., the Patent literature 1). This polycrystalline silicon rod includes at least four regions having different fine structures on the radial cross section of the rod. Moreover, this polycrystalline silicon rod is configured so that a polycrystalline thin rod exists within a region A of the innermost polycrystalline rod center, and no needle-shaped crystal exists or only a bit of needle-shaped crystals exists or exist within a region B of polycrystalline silicon deposited around the thin rod. More specifically, the thin rod of the region A is formed so as to have a regular square in cross section having a size of sides of 5 to 10 mm, and the diameter of the region B is formed so that it is more than 30 mm. Moreover, the area percentage of the needle-shaped crystals within the region B is less than 1%, the length of the needle-shaped crystals is 5 mm or less, and the width thereof is 1 mm or less. Moreover, the polycrystalline silicon rod is configured within the outside region D thereof so that the area percentage of the needle-shaped crystals is less than 7%, the length of the needle-shaped crystals is less than 15 mm, the width of the needle-shaped crystals is less than 2 mm, and the length of the micro-crystals of the matrix is not above 0.2 mm. Further, the polycrystalline silicon rod is configured between the regions B and D so that there exists a mixed region C such that the crystal structure smoothly shifts from the structure within the region B to the structure within the region D.
In the polycrystalline silicon rod constituted in this way, since a bit of needle-shaped crystals of a small size within the region B are completely molten by heating in the subsequent FZ method, it is possible to eliminate a deficiency such that any defect may take place within the single crystal silicon after unmolten needle-shaped crystals or the remaining parts thereof are passed through the molten zone. Moreover, within the outside region D, the highest thermal stress may take place in the polycrystalline silicon rod during deposition process. It is to be noted that the strength is enhanced by microcrystalline matrix to a degree such that any breakage or crack does not take place within the rod region and the bridge region except for the rod bottom part in contact with electrodes. Further, the mixed region C taking place between the inside region B and the outside region D has a crystal structure smoothly shifting from the structure within the region B to the structure of the region D, and this mixed region C exists within the diameter region of 30 mm to 120 mm.